Processes for the production of fibrous structures

ABSTRACT

Process of and apparatus for the production of fibrous and/or like structures, the process comprising subjecting to a softening treatment and a shrinking treatment a fibrous base formed of at least two kinds of fibers one of the said kinds of fibers being retractile with respect to the other of said kind or kinds of fibers.

United States Patent lnventor Henri Robert Lissalde Rouen, France Appl. No. 715,324 Filed Mar. 22, 1968 Patented Oct. 26, 1971 Assignee Papeteries Navarre Paris, France Priority Apr. 4, 1967 France 101,444

PROCESSES FOR THE PRODUCTION OF FIBROUS STRUCTURES 7 Claims, 2 Drawing Figs.

us. Cl 156/85, 156/85 1m. c1 B32b 31/24, B32b 31/26 Field of Search 156/84, 35

[56] References Cited UNITED STATES PATENTS 3,159,525 12/1964 Finger 158/85 X 3,180,775 4/1965 Sexsmith 156/85 3,214,323 8/1965 Russell et al 156/85 X 3,395,066 7/1968 Tucker 156/85 X Primary Examiner-Benjamin R. Padgett Assistant Examiner-S. R. Hellman Attorney- Young & Thompson ABSTRACT: Process of and apparatus for the production of fibrous and/or like structures, the process comprising subjecting to a softening treatment and a shrinking treatment a fibrous base formed of at least two kinds of fibers one of the said kinds of fibers being retractile with respect to the other of said kind or kinds of fibers.

PROCESSES FOR THE PRODUCTION OF FIBROUS STRUCTURES BACKGROUND OF THE INVENTION 1. Field of the invention This invention relates to improvements in processes of and apparatus for the production of fibrous and/or like structures.

2. Description of Prior Art Certain fibrous and/or like structures for example those used in technical fields such as filter paper, should possess a great true surface under a small apparent surface, which is accomplished by means of conventional folding, embossing, crimping or other methods. In other fields, such as domestic, clothing, and industrial, fibrous materials or structures are required having characteristics such as: a low apparent density, a high liquid absorption and desorption capacity, satisfactory elasticity, high compressibility, a pleasing appearance, and satisfactory printability. The method of producing these characteristics in fibrous structures is sometimes referred to as textilization." The term base" as used in this specification means a sheet or web consisting of fibers or of fibers and particles.

It is known that certain fibers of synthetic origin in particular, are capable of shortening to a substantial degree under chemical processing or heat treatment, and this property has already been exploited for compacting various bases intended for use as felt or as artificial leather, and for increasing their density or breaking strength. By introducing such fibers into the composition of a base and by appropriately treating these fibers, the applicants have found that it is possible in certain conditions, to ensure that these special retractile fibers, sometimes referred to as FR, by their physical retraction modify the structure of the base which shrinks in surface whilst acquiring thickness, with superficial crimping.

The conditions governing the satisfactory application of this technique for textalization of bases such as, for example, unwoven fabrics, obtained by a wet or dry method, apply more specifically in respect of the composition of the base, its texture, application of the retractive treatment, softening of the fibers, and if appropriate, to the method of application of a polymerization or stabilization stage for the bonding agent, and to the position of this stage in the sequence of operations.

The main object of the present invention is to provide a process of and apparatus for so-called textilization to produce the aforesaid characteristics in a simple, reliable and convenient manner in fibrous and/or like structures or bases.

SUMMARY According to the present invention there is provided a process for the production of fibrous structures comprising the steps of forming a crude base from at least two kinds of fibers, one of said kinds of fibers being retractile with respect to the other of said kind or kinds of fibers so that the said at least two kinds offibers are intermeshed or intermingled in the formed crude base, subjecting the said crude base to a softening treatment to soften the said at least two kinds of fibers and subjecting the said crude base to a shrinking treatment to cause shrinkage of the said retractile fibers and contraction of at least one of the major dimensions of the treated base and an increase in thickness of the said treated base.

it will be appreciated that the intermingled and relatively unshrinkable fibers tend to pile up due to the contraction of the retractile fibers, and thus acquire a wavy form, which causes wrinkling or crimping within the very mass of the base, with an increase in thickness and with superficial crimping if appropriate.

The texture of the base should be sufficiently loose and homogenous to permit individual mechanical displacement (shortening and flexing) of each FR fiber, and uniform gathering up of the other intermingled fibers. These are advantageously folded over each other, in such manner as to be displaced in unit instead ofslipping relative to each other.

In a preferred embodiment of the invention, the pliability of the base is improved by forming areas of reduced density therein, or so-called hinge" areas. To this end, the base is formed from a fibrous suspension which is drained through a meshwork partition, the hinge areas being produced opposite the gaps in the meshwork. If applicable, jets of water are injected into the fibers piled up in alignment with the draining area and this for the same purpose, for example as described in the applicants copending US. Pat. application Ser. No. 705,735 filed Feb. 15, 1968.

Depending on the application of the treated structure, the base is provided with the required degree of pliability, by allowing adequate humidity to subsist therein during the period in which the base undergoes an operation including the presence of a humid phase, or by introducing water into the base and stabilizing it by means of humidity-retaining products, or by heat softening the base which may or may not contain a binder.

Preferably the base is softened by saturating it with steam, preferably saturated steam, at a temperature which is lower than and preferably close to the temperature of retraction of the FR fibers having the lowest temperature of retraction (in the case of a mixture of several types of FR fibers). Conventional steam generators may be used.

The retracting operation of the process of the invention is thus performed on a pliable base and is preferably carried out immediately after a softening stage employing steam. To this end, the base is treated with known chemical products, or else is thermally treated with heat at a sufficient temperature and for a duration adequate to cause its partial or total retraction depending on the desired application. The heat is supplied to the base by means of hot air, hot water vapor, infrared radiation, hot fluid, which have substantially none or no wetting capability with respect to the base, or any other appropriate source of heat. The quantitative extent, nature, temperature and duration of the chemical or thermal treatment determine the proportion percent of retraction undergone by the base. The proportion percent of the retraction is expressed in the following ways;

For a base comprising directionally positioned fibers, by different dimensional shrinkages in the direction of production and transverse direction;

For a base lacking a preferential direction of the fibers, by the resulting reduction in surface, with omnilateral contraction in size;

For all bases, by the increase in thickness and the modification in the apparent density.

According to the nature of the FR fibers or the mixture of FR fibers of different origin, the process of the invention renders it possible to perform simultaneously the softening action and the retraction action by means of a single heat source and particularly by means of steam, the latter being used in one or more successive or simultaneous different physical conditions.

In certain cases, a binder is incorporated in the fibrous structure, which improves adhesion between the fibers, and this binder is stabilized after shrinkage, in such manner as to ensure permanence of the crimping of the fibers and as to promote the elasticity of the base.

The binder may be fibrous and of natural origin, or of synthetic or artificial origin, or it may be formed for example by emulsions, solutions, or powders. its selection depends on the final purpose of the base, and may be determined so that the crude base retains a pliability which promotes shrinkage.

If the shrunk base comprises a polymerizable, condensible or reticulable hinder, the polymerization condensation or reticulation stage occurs after shrinkage, irrespective of the stabilization method adopted. This operation has the result of solidifying the structure comprising fibers and binder and, as stated, of maintaining the crimping of the fibers in such manner that, after having undergone mechanical stresses for example tension, compression, and torsion (in a degree commensurate with and customary for the use'made of the object in question). the sheet is deformed elastically and returns to its initial state. This operation also has the result of stabilizing the binder in its final chemical form and thus of endowing the same with the final characteristics required.

In certain applications, the polymerization is performed according to conventional methods, such as heating the base with hot air, by infrared radiation, or by means of heating drums, but in this invention the polymerization is carried out after shrinkage. it will be appreciated that polymerization, condensation or reticulation may cause a secondary shrinkage, which must be taken into account in the overall dimensional change of the base between its formation and the end of its various treatments. This secondary shrinkage is known beforehand, and is a function of the shrinking operation as such.

After the shrinking stage, followed by polymerization or not, the base may possess excessive stiffness, a rough surface, an unpleasant appearance and technical characteristics which are neither adequate nor stabilized. In order to overcome these disadvantages the base is subjected to the following operations;

Calendering or sleeking, is performed in the cold or under heat, under controlled pressure and temperature so that the base is levelled and softened by articulation of the structure of fibers and binder fixed by polymerization;

Steeping consist of dampening the base sufficiently with water, for example by soaking and expressing, carried out as part of a washing operation. During the steeping operation a variety of types of products having functions may be introduced into the base such as dyes, blueing" agents, plasticizers, softeners, scents. The essential purpose of steeping is to release the internal strains of the sheet by swelling certain fibers with water and by saturating the interstitial spaces of the composition with water. The base thus becomes soft and inert;

Stabilization of the shape of the base consists of placing the fibrous structure of the base under internal strain again whilst keeping the base in the plane condition it is required to possess at the end of the operation. This restoration of strain is performed by evaporating the water from the base and the plane condition is maintained by mechanical compression. This operation may be performed analogously to the pressing of textile materials in industry. A drying apparatus, as used in papermaking, may also be advantageously employed, in which the continuous sheet or web is applied powerfully by means of felt rollers against heating drums, and this alternately against each of its surfaces. A single drum may be employed, or adequate drying capacity and equipped with a pressing and drying felt roller or pad. The tension of the felt or cloth applying the sheet against the drum or drums is adjustable, as is the surface temperature of the drums, and their relative speeds.

In certain cases, the steeping and stabilization stages may be omitted, ifthe shrinkage is performed using a hot fluid.

The textilization process of the invention is also applicable to fibrous structures such as mats, and carding fleece obtained by a dry method, as well as to those produced by any other method than the so-called papermaking" method, in which the constituent fibers are placed in suspension in a liquid usually water in order to be intermingled in the final form ofa more or less dense continuous sheet or web of greater or lesser thickness. It is pointed out however that this process is. of special interest in its application to the bases produced by means of the process and device described in the US. Pat. application hereinbefore referred to. These bases, obtained by compression into a web of an agglomeration of omnilaterally directed fibers, have a structure of intermingled fibers, folded over each other, which facilitates textilization since it ensures solidity and homogenous distribution of flexible connections between the fibers.

The shrinking operation may be performed immediately after production of the crude base, and may be incorporated in a continuous process beginning with the bulk fibers and ending with the textilized product.

The process of the invention renders it possible, by increase in thickness with or without appreciable surface crimping, to textilize crude bases of very different weight per unit area, which may amount to between SgJm. or less and 1000 gJm. or more, the thicknesses corresponding to these weights are appropriately smaller than 0.01 mm. and greater than 1 mm.

Reference will now be made, to the following nonlimitative example of the process of the invention.

The starting material is a base comprising intermingled fibers, whose composition by weight includes:

45 percent of low denier count (1.5 to 5) viscose fibers;

15 percent of cellulosic fibers (for example soda-digested pine fibers) or other fibrillable fibers such as "polynosic" fibers;

20 percent of retractile fibers of the chlorofibre type for example, having a temperature of retraction of 70 -75 C.;

20 percent of a flexible binder, for example consisting of a self-reticulating polyacrylic resin.

A base of this kind, for example possessing a weight of 60 g./m. shrinks so as to weigh l00g.lm.after having undergone a thermal textilizing operation bringing the base into contact with saturated steam for 8 to 10 seconds so that the temperature of the steam at the surface of the base reaches C. after the first 2 to 3 initial seconds of this dwell period.

The invention also comprehends apparatus for carrying out the process of the invention said apparatus comprising an enclosure forming a softening and shrinking tunnel for a fibrous base, conveyor devices for conveying said fibrous base through said enclosure, means for softening and means for shrinking said fibrous base, each of said means being disposed within the said enclosure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows diagrammatically, by way of example, apparatus for carrying out the process according to the invention; and,

FIG. 2 shows an alternative form of the apparatus of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, this shows an extensively perforated endless conveyor belt 1 of plastics sheet material or metal fabric, having along its path drying elements 2 and preheating elements 3, as well as all devices required for guiding, tensioning, smoothing.

The top portion of the web or belt, is tensioned between the rollers 4 and 5 and may advantageously occupy a nonhorizontal position, for example sloping in such manner that the roller 4 is situated before the roller 5 in the direction of travel of the top run," and at a greater height than the roller 5. The roller 5 is driven causing the belt to advance at a variable speed and is equipped with a pressing roller 6.

A shrinking tunnel 7 is formed by an enclosure with heated double-jacket walls of the anticondensation type, through which the conveyor belt travels, and may be divided as shown into internal compartments, by partitions 78 illustrated by dotted lines, in such manner that the different compartments may be optionally supplied with vapors at different temperatures, have a negative pressure established in them, or receive hot air.

A hood or canopy 8 having a heated double wall, encloses the belt and tunnel and is provided with an extraction fan.

A circuit 9 for intake of the crude or unshrunk base 10 comprises a rotary intake press formed of rollers 11 driven at a variable speed corresponding to the speed of the belt, as a function of the degree of shrinkage required and caused in the apparatus, the speed of ejection of the shrunk base being lower than the intake speed of the unshrunk base.

Hot fluid is fed into the tunnel at 7A, and escapes from the same through the ingress and egress orifices of the base 10.

It is advantageous that no excessive mechanical resistance caused by gravity, pressure, tension or friction applied to the base, should be opposed to the force of retraction of the FR fibers when this force begins to operate. To this end, the sheet or web placed on a conveyor belt, should have as low as possible a coefficient of friction with respect to the latter, whether in the shrunk condition or not. it is equally advantageous for the top run bearing the base to slope in order to reduce the frictional forces engendered by the intrinsic weight of the base 10. These frictional forces are eliminated entirely in the case of a vertical base, but in this case, the tractive forces engendered by the direct action of the intrinsic weight of the base may become excessive. The optimum conditions are thus established by a sloping position between the vertical and the horizontal positions.

The friction between the sheet or web and the belt is frequently greater for the shrunk part than for the unshrunk part. From this point of view, the apparatus of FIG. 1 is particularly advantageous, because the force of gravity has the result of impelling the unshrunk part towards the tunnel and of reducing or even cancelling the tractive force referred to above, which favors the shrinking of the base.

The conveyor belt may be a porous felt of a permeable cloth.

The apparatus of the invention may comprise several variants according to which for example the sheet or web undergoing shrinking has hardly any or no mechanical contact with a solid body. in this case, the base may be arranged in a vertical, horizontal or oblique position, and in each position it is advantageous for the stretch between contact points to be very short, so that the shrinking action is not affected by any opposing force.

it is equally advantageous to perform the shrinking operation in an environment which is gaseous and pulsates in such directions that, in respect of the sheet, it protects the latter against experiencing any mechanical stress of a force liable to oppose shrinkage.

Referring to FIG. 2, this shows a base 12 moving in the direction of the arrow F in an enclosure 13 under saturated vapor pressure between a deaerating press 14 and an outlet press 15, with a vapor or steam feed inlet at 16. Within the enclosure, the base rests on rotary bars 17 heated to prevent condensation.

The press 14, formed by rubber or other rollers, compresses the base and expels the air, with the result of steeping it in vapor as soon as it is decompressed, since the outlet of this press is situated within the enclosure 13. Penetration of air abreast of the rollers is prevented by means of seals which are not illustrated, or by establishing an overpressure in the enclosure.

The output of the machine may be increased by placing several sheets one on the other, which are shrunk at the same time, or else by continuously or intermittently piling up the sheet or web on the conveyor belt in the form of vertically juxtaposed loops, or of loops laid one upon the other.

In the apparatus of the invention, the treatment by means of saturated water vapor engenders uniform softening of the base, followed immediately by an input of heat causing shrinkage of the fibers Owing to this preliminary softening, the shrinkage of the base occurs uniformly, without destroying the connection between the fibers, and without forming lumps.

I claim:

1. A process for the production of fibrous structures comprising the steps of forming a crude homogeneous base of unbonded fibers from at least two kinds of fibers in intimate random admixture with each other, one of said kinds of fibers being retractile with respect to the other fibers so that all the said fibers are homogeneously intermeshed or intermingled in the form crude base, subjecting the said crude base to a softening treatment to soften the said at least two kinds of fibers and subjecting the said crude base to a shrinking treatment to cause shrinkage of the said retractile fibers and contraction of at least one of the major dimensions of the treated base and wrinkling or crimping of the relatively unshrinkable fibers within the mass of the base while substantially preserving the contours of said base.

2. A process according to claim 1 wherein, the said at least two kinds of fibers are bent over each other during the said forming step.

3. A process according to claim 1 wherein areas of reduced density are produced in the said crude base during the said forming step.

4. A process according to claim 1 wherein the said softening treatment comprises treating the said fibers of said crude base with water vapor, said water vapor being at a temperature which is lower than the shrinkage temperature of the said retractile fibers.

5. A process according to claim 1 wherein the said shrinkage treatment of the said softened crude base consists of thermally treating the said softened crude base.

6. A process according to claim I wherein the said shrinkage treatment of the said softened crude base consists of thermally treating the said softened crude base by using water vapor as the source of heat.

7. A process according to claim 1 wherein a binder is incorporated in the crude base prior to the softening and shrinking steps and wherein said binder is made binding after said softening and shrinking steps. 

2. A process according to claim 1 wherein, the said at least two kinds of fibers are bent over each other during the said forming step.
 3. A process according to claim 1 wherein areas of reduced density are produced in the said crude base during the said forming step.
 4. A process according to claim 1 wherein the said softening treatment comprises treating the said fibers of said crude base with water vapor, said water vapor being at a temperature which is lower than the shrinkage temperature of the said retractile fibers.
 5. A process according to claim 1 wherein the said shrinkage treatment of the said softened crude base consists of thermally treating the said softened crude base.
 6. A process according to claim 1 wherein the said shrinkage treatment of the said softened crude base consists of thermally treating the said softened crude base by using water vapor as the source of heat.
 7. A process according to claim 1 wherein a binder is incorporated in the crude base prior to the softening and shrinking steps and wherein said binder is made binding after said softening and shrinking steps. 